The present invention relates to an ultrasonic probe in which a group of piezoelectric elements that is a source of ultrasonic waves oscillates in the short-axis direction to obtain a three-dimensional image (hereinafter called a “short-axis oscillating probe”) and, in particular, to a short-axis oscillating probe of a simple configuration in which the operational noise of the probe while operating is minimized to remove that source of discomfort to the patient.
1. Field of the Invention
A short-axis oscillating probe that is known in the art obtains a three-dimensional image by electronically scanning a group of piezoelectric elements in the long-axis direction of the probe and also by mechanically scanning (oscillating) the group of piezoelectric elements in the short-axis direction thereof (see Japanese Patent Laid-Open Publication 2006-346125 (prior-art example 1), Japanese Patent Publication No. TOKKO-HEI 7-38851 (prior-art example 2), and Japanese Patent Laid-Open Publication No. 2003-175033 (prior-art example 3)). Since components such as wiring (connective wires) and scan circuitry of this type of short-axis oscillating probe can be configured simply, in comparison with a matrix type of probe in which piezoelectric elements are arrayed horizontally and vertically to provide a two-dimensional electronic scan, this probe can be implemented easily.
2. Description of Related Art
A prior-art example of a short-axis oscillating probe is shown in FIG. 2, where FIG. 2A is a section taken along the long-axis direction thereof and FIG. 2B is a section taken along the short-axis direction thereof.
The short-axis oscillating probe of this prior-art example is provided with a group of piezoelectric elements 1 and a rotational mechanism 2, as shown in FIG. 2A. The group of piezoelectric elements 1 is arrayed on a backing member (not shown in the figure), with the widthwise direction of a plurality of card-shaped piezoelectric elements 1a aligned in the long-axis direction and also the lengthwise direction thereof aligned in the short-axis direction. The backing member is affixed to the top of a base 4, which is formed in a convex dome shape in the long-axis direction, with the configuration being such that the group of piezoelectric elements 1 is curved outward in the long-axis direction.
A flexible substrate 5 that has been connected electrically to the group of piezoelectric elements 1 over the entire region of the probe in the long-axis direction thereof is lead out downward from one end side of the probe in the short-axis direction. In this case, a conductive path 5a of the flexible substrate 5 is connected electrically to a drive electrode of each piezoelectric element 1a. The two could be connected directly, as shown in FIG. 2, or the drive electrode of each piezoelectric element 1a could be connected indirectly to the conductive path 5a by means such as silver foil and conductive wiring.
The rotational mechanism 2 shown in FIG. 2 comprises a retaining plate 6, a case 7, a first bevel gear 8a, a second bevel gear 8b, a rotational shaft 9, and a drive motor 10 that has been attached to a framing member 7b. The retaining plate 6 has leg portions 6a and 6b on the lower surface thereof on both edge sides in the long-axis direction, and the base 4 holding the group of piezoelectric elements 1 is affixed to the upper surface thereof. Center shafts 11a and 11b that penetrate through the corresponding leg portions 6a and 6b are provided in the long-axis direction (on the line X-X in the horizontal direction shown in FIG. 2A), on bearings 11c and 11d. The leg portions 6a and 6b are provided to be freely rotatable with respect to the center shafts 11a and 11b. 
The case 7 is formed to be concave in section with the upper surface thereof being open, and projecting ends of the center shafts 11a and 11b that protrude from the leg portions 6a and 6b are connected (affixed) to peripheral walls of the case 7. A slit 12 is formed in the long-axis direction of the bottom wall of the case 7, and the flexible substrate 5 from the group of piezoelectric elements 1 is lead out to the exterior therethrough. A material such as a synthetic resin 13 is embedded in the slit 12 to seal the same.
The first bevel gear 8a is provided on the inner surface of the leg portion 6a, below the center shafts 11a and 11b, and has teeth in an arc (a fan shape) with a peak thereof at the lower end in the vertical direction. The second bevel gear 8b is borne on the free end side of the rotational shaft 9, which is in the vertical direction perpendicular to the center shafts 11a and 11b (the line X-X), and engages with the first bevel gear 8a to rotate in the horizontal direction (the X-X direction). The rotational shaft 9 is lead out from the bottom wall of the case 7 and is sealed by sealing 14, and the other end thereof is linked (meshes) with the drive motor 10 by means such as metal gears 15a and 15b. 
In this prior-art example 1, the first bevel gear 8a and the second bevel gear 8b are formed of metal, and the diameter of the equivalent circle of the arc-shaped teeth of the first bevel gear 8a is greater than the diameter of the second bevel gear 8b. In addition, the diameter of the metal gear 15a affixed to the rotational shaft 9 is greater than the diameter of the metal gear 15b of the drive motor 10.
By making the gear ratio from the drive motor 10 to the first bevel gear 8a greater in this manner, this configuration ensures that the rotational force (torque) of the drive motor 10 is increased and maintained in the transmission of drive to the first bevel gear 8a. Note that a cover (not shown in the figure) that encloses the group of piezoelectric elements 1 is provided for the case 7, the group of piezoelectric elements 1 and other components are hermetically sealed therein, and the interior of the case is filled with an ultrasound transmission medium such as oil.
In the thus-configured prior-art example, the rotation (oscillation) of the second bevel gear 8b that configures the rotational mechanism 2 horizontally to left and right causes the first bevel gear 8a to oscillate with respect to the vertical plane so that the peak thereof inclines upward to the left or right from the center. In other words, the peak of the first bevel gear 8a rotates and oscillates to the left and right of the vertical direction acting as center. Thus the leg portions 6a and 6b of the retaining plate 6 rotate and oscillate to the left and right with respect to the center shafts 11a and 11b, and also the group of piezoelectric elements 1 rotate and oscillate to the left and right in the short-axis direction, in the opposite directions thereto. In addition, the rotational angle in the short-axis direction from a reference position is detected by a rotational angle detection mechanism (not shown in the figure) for the rotational shaft 9, thus obtaining information from an object to be detected (organism).